Necesidad para el control de la temperatura
One inherent feature of LifeSpan, and most other commercial MAP products, is that as temperature
increases the gas permeability of the film package only increases slowly. However as temperature
increases, the respiration rate of the packaged produce increases rapidly. Thus an MAP design
that has equilibrium between package permeability and produce respiration at a specific
temperature loses that equilibrium as the temperature increases. As the respiration rate increase is higher than the package permeability increase the atmosphere inside the package will modify further away from air. At some point, this increasing modification of the atmosphere will switch the produce into anaerobic respiration. When this happens, produce quality will begin to decline rapidly.
Anaerobic respiration also has a high respiration quotient, so that the carbon dioxide level will continue to rise with anaerobic respiration. This pushes the atmosphere further away from aerobic conditions and virtually ensures that the produce will not return to aerobic respiration, even if the temperature declines to the original design value.
Anaerobic respiration causes a build up of aldehydes and alcohol in the produce tissue. After a
relatively short period of anaerobic respiration, the produce will become noticeably tainted and it will have off-odours.
Hence there is a need to restrict the operating temperature range for any LifeSpan design. For
most applications, a range of 5°C (8°F) is achievable without harming the produce, however the
temperature range is dependent on the absolute rate of produce respiration and how rapidly this
alters with temperature.
We always print the designed temperature range on every LifeSpan product to ensure that users
are familiar with the appropriate, but restricted, temperature range. We also try to avoid LifeSpan designs with oxygen levels targeted below 4%. In most properly designed applications, anaerobic respiration doesl not switch in above 2% oxygen. Thus we build in a safety buffer to take account of occasional short term losses in temperature control. We will usually prove that the safety buffer is useful and adequate in the same trials that we prove the design will function safely over the design temperature range. These proofing trials also confirm the expected postharvest life is achieved, with some produce held at the upper end of the design temperature range.
